This story started with me poking around the Parts Express website 6 months ago - a budding speaker builder with only a couple of builds under my belt: A pair of Overnight Sensations in Zebrawood built recently, and a set of KEF speakers built ages ago during my junior high-school days growing up in Denmark. When I stumbled upon a factory buyout of the Vifa D19TD-27-08 tweeter made in the original factory in Videbęk, Denmark, about 70 miles from my little hometown, I knew I had to design a speaker around it.
I'm a Danish-American (amateur) choral singer with an Italian-America wife who is a coloratura soprano, so reproduction of voices and accurate imaging were obvious top priorities. The project name "Koloratur" - the Danish word for coloratura - also came naturally.
The little Vifa isn't happy going much below 3 kHz, and I didn't want to embark on a three-way for my first design, so I decided to go with the new Dayton Audio RS-150P-4A paper cone woofer that has a smooth frequency response and is small enough to have reasonable dispersion above 3 kHz. So like my marriage, this project is proudly combining parts that originate in Jylland (the western peninsula of Denmark) and the American Midwest.
After running simulations in WinISD, I decided to sacrifice some max SPL in return for bass extension and chose a ported design tuned at 48Hz using the 0.56 cubic feet pre-made cabinet from PE. As you can see from the picture, I mounted the drivers as closely as possible, asymmetrically on the baffle to (hopefully) smooth out any diffraction bumps. I applied some extra (red oak) bracing and bitumen sheets to deaden the baffle and cabinet, and lined it with sonic barrier.
Finally, to make it easy to tinker, tune, and learn, I chose to go the active route with a miniDSP 2x4 HD active crossover, and also kept things modular and flexible by not putting any electronics in the speaker cabinets (4-pole speakON connectors are awesome). I ended up crossing them at 3.5 kHz with 48 dB/octave slopes and applied bafflestep compensation and various corrections to straighten the response of the drivers. I also added a 30 Hz 48 dB/octave high-pass filter on the woofers to limit excursion from low-frequency material. I know I'll probably keep tinkering with the filters settings forever, but I have attached a curve measured in my garage at ~1m with the umik1 and REW reflecting the current state of affairs. It's reasonably flat from 40 Hz to 20kHz. I have the opportunity to measure them in an anechoic chamber soon, so hopefully I can get a clearer picture then.
After some basic "dialing in", I'm quite impressed with the result (I'm obviously biased). The imaging is really pinpoint accurate and has great depth. Voices and piano sound beautifully clean and detailed. In rock & pop I discover quite a few new details and instruments are clean and nicely separated.
The next step is choosing a finish and make them look as pretty as they sound.
P.S. If you look carefully, you'll notice that the (excellent) beer consumed during the making of these speakers is from Grand Rapids, MI.